Alternative energy conversion technologies have attracted a great deal of attention over the years for their utility and various applications.1-6 Among these technologies, proton exchange membrane fuel cells (PEMFCs) that combine high-energy density,7-8 conversion efficiency9 with versatile mobile and stationary applications,10 and minimal emission of CO2,4 have been studied extensively.5, 11-21 
Proton exchange membranes (PEMs) should have multiple attributes. First, the body of the membrane should have physical properties consistent with its function, for instance essential properties such as mechanical strength, toughness and flexibility. They should also be highly resistant to the highly acidic media to which they are exposed as they are expected to function for prolonged times (months to years). Furthermore, exposure to water at temperatures varying from ambient to high temperatures (150° C.) is to be expected. The permeability for water and other fuels must be controllable subject to fine tuning. For instance, buildup of water or fuels at the electrodes should be avoided so that a membrane would have to mediate with efficient water management and that of other liquid fuels such as methanol. For instance, major swelling of the membranes with water or other fuels resulting in a change of membrane properties must be avoided so that the main body of the membrane should be solvophobic. However, the electrical resistance of the membrane must be high in order to not short circuit the device, whereas the efficient permeation of hydronium ions from anode to cathode is crucial. On the other hand, the transport of methanol or other fuels from anode to cathode must be minimal. Hence, the membranes must be polymer composites with each component providing a set of desirable but largely orthogonal properties.
Among the various fuel cells, the direct methanol fuel cell (DMFC) has great potential as a stationary and portable device.22-31 One of the key components that determine the DMFC performance is the proton exchange membrane (PEM) among which NAFION®®, a perfluorocarbon sulfonic acid copolymer, is widely used due to its high proton conductivity and good thermal stability.32 However, NAFION® has some shortcomings in DMFC and other applications as it is prone to both spontaneous and proton mediated methanol diffusion toward the cathode (“methanol crossover”) causing as much as 40 percent methanol loss.32-33 The high cost of the NAFION® membrane (20-30% of DMFC cost) is an additional limitation.34 
Over the past few years, the quest for higher performance (higher proton conductivities, better thermal stabilities and mechanical properties) and lower cost alternative membranes has continued.2, 5, 9, 13, 23, 30, 33, 35-40 Recent reports have included grafting or embedding polystyrene sulfonic acid (PSSA) onto inert fluorinated polymer matrixes, such as poly(vinylidene fluoride) (PVDF), and polytetrafluoroethylene (PTFE), giving DMFC membranes with lower methanol cross-over.33, 35, 41-44 Sulfonated hydrocarbon PEMs, including sulfonated polystyrene and its derivatives, sulfonated poly(arylene ether)s, sulfonated polyimides, and sulfonated polyphosphazenes are synthesized based on either post-polymerization functionalization such as sulfonation or direct copolymerization of sulfonated or other functionalized monomers.40,45 Prakash et al. used a semi-interpenetrating polymer network (sIPN) by swelling PVDF membranes in styrene and divinylbenzene solution followed by an AIBN initiated polymerization and the subsequent sulfonation.33, 46 Also, Muftuoglu et al.41, 47 synthesized membranes based on PVDF-g-polystyrene followed by sulfonation. However, there are several major drawbacks of post-modification methods. These include the lack of reproducible control over the degree of sulfonation, the location of the sulfonate groups, the often inevitable side reactions due to more reactive sulfonation reagents and/or -conditions, and, perhaps, polymer degradation.20 Although membranes prepared by post-polymerization sulfonation showed higher proton conductivities than NAFION® under high humidity conditions at 30-120° C., ether excessive water swelling and membrane instability at high temperatures34,41 or mechanically deficient in the dry state and poor reproducibility emerge as new problems.13, 23, 30, 40 
Given these requirements, successful membranes typically have a large hydrophobic content (60-90 wt. percent) but are selectively permeable, for instance, through the presence of percolating hydrophilic domains. This could be achieved using a number of synthesis methods including but not limited to: (a) copolymerization of a hydrophobic monomer and a hydrophilic comonomer that self-assemble spontaneously into hydrophilic/hydrophobic domains under varying conditions. This also includes block copolymers consisting of hydrophobic and hydrophilic blocks.48-49 (b) A hydrophobic polymer grafted with hydrophilic chains that self-assemble under suitable conditions.47, 50 (c) interpenetrating polymers blends through the polymerization of a precursor monomer in the bulk phase of another giving an interpenetrating network followed by the functionalization (i.e. sulfonation) to give a hydrophilic phase anchored in the bulk material.33, 35,42 (d) Blends of carefully chosen hydrophobic and hydrophilic polymers followed by later crosslinking if required.51-53 
The wide selection of methods and materials and low processing costs seem to make blending an attractive but challenging option. Blends from hydrophobic and hydrophilic components typically produce materials with poor properties due to the inherent incompatibilities of hydrophobic and hydrophilic polymers that typically cause the formation of large domains that, in turn, give rise to poor mechanical properties as well as poorly controlled diffusion.54-55 Thus, direct blending of poly(sodium styrene sulfonate) (PSSNa) with PVDF or the embedded polymerization of SSNa in PVDF solution56-57 gives highly heterogeneous and hence inferior membranes with weak mechanical strengths due to the poor PVDF-PSSA compatibility and hence phase separation at the micron level or larger giving heterogeneous materials.56,58-59 
Proton exchange membranes (PEMs) are finding applications among other things in fuel cells using hydrogen or organic fuels such as methanol or ethanol and combine high energy densities and conversion efficiencies with minimal emission of CO2. The invention set forth describes well established principles for polymer solvent interactions as a guideline for the use of binary polymer blends that are partially or fully compatible depending on the temperature. This modular design, at least in principle, is extremely versatile, flexible and potentially economical given the high cost of NAFION® membranes, the current “gold standard” for membranes in PEM fuel cells.
Accordingly, there is a need for improved proton exchange membranes formed from polymeric blends.